Genetic discrimination of brackish and freshwater populations of Eurasian perch (Perca fluviatilis L.) in the Baltic Sea drainage: implications for fish forensics

Over recent years a growing number of studies suggest that both unregulated and illegal fishing can lead to the unsustainable exploitation of populations or species. For developing biologically sound management and conservation actions and to effectively fight against the illegal fish trade, it is crucial to understand the spatial and temporal patterns of genetic diversity of commercially important fish species. In this study we characterized for the first time the population structure of Eurasian perch at both freshwater (Lake Peipus) and Baltic Sea locations, representing important targets of commercial perch fisheries in Estonia. We also evaluated the effectiveness of individual and group-based assignment tests to identify the genetic origin of fish at different geographic scales. Results of our study showed low genetic divergence among sample sites, which resulted in a low self-assignment accuracy of individual fish to their sampling locations (mean 36.7%). However, the assignment accuracy at the regional level was considerably higher (Baltic Sea: 84.9%; Lake Peipus 88.0%). When assuming an unmixed origin of the group of individuals, it was possible to identify the brackish and freshwater origin of perch with very high confidence (log10 LR > 3) if the sample size exceeded 15-20 individuals. Our study demonstrates the power of highly variable genetic markers to distinguish between the two commercially most important Eurasian perch stocks in Estonia and the usefulness of assignment tests to successfully identify the genetic origin of fish. We expect that the developed microsatellite-based reference database together with the described analytical framework provides an important tool to more efficiently combat against illegal fishing and fish trade. (C) 2016 Elsevier B.V. All rights reserved.